HP1740a option 101 reversal?

[eucaly21]

Hi.

I recently acquired an HP1740A oscilloscope which had the option 101. This was for use with a data analyzer, but in place of the XY or A vs B mode. If anyone here has encountered this then you know what I am asking. Has anyone here successfully done this reversal?

I know its been done, I found a sparse posting from another site from years ago, but he left no details on how he did it.

[eucaly21]

Unbelievable! I worked on this all day yesterday before posting here, and after I posted a light bulb went off, one more thing I could try. And it worked. If anyone runs across an option 101 1740A, the xy mode can be restored with 0 additional parts. I didn't photo document the job but I do have some photos which I'll share shortly, along with what I did.

[eucaly21]

Ok turns out I took more photos that I remembered. All this can be discerned form the service manual, but hopefully this writeup will save someone some time, or encourage someone to proceed. Again, this modification is necessary if you have a HP1740a with option 101 and want to use the A vs B (XY mode).
Overview photo showing wires that will be removed.

. First, check to see that to make sure your A3 board has these components: a3c77 capacitor, a3cr28 diode, a3Q21 transistor(actually marked on board), a3139,140 resistors. The sm states that these components are omitted, but at least on my unit, were present.

clip wires, yel/pink. remove 2 resistors, the ones closest to clipped wires (a3 board).

Clip blue and white wires from a7 board.

Remove 4 diodes from a7 board, marked "option."

On a3 board, move one diode marked option, and solder it next to row of 3 other identical diodes.

Here is the modified a3 baord.

Here is the interface assembly board that comes on the option 101 units. Notice all the components? The regular interface board has none of these.

This last step is the one I initially didn't think to do. 4 traces on the interface assembly must be cut. First I tried to desolder the 3 traces that terminate mid board, but I didn't succeed in  breaking contact until I used a small drill PARTIALLY drill through board. Finally I cut the last trace with a small file. I'm sure you can think of a cleaner way to do this, but this is what I did.

Playing some music through unit in A vs B mode!

[electronix27]

Great article.  Picked up one of these that I am currently working on.  This scope also has the 101 option that I definitely don't want in lieu of the A vs B function (XY mode).  I have the Service Manual, but this is very helpful.  I was able to find the connector only 66540 board, instead of using the populated, 101 option 66541 board.

Thanks bro
Russell